#border{
    position: absolute;
    border: 2px solid red;
    right:10%;
    top:10%;
    left: 10%;
    bottom: 10%;
}
.center {
    width: 0px;
    height: 0px;
    position: absolute;
    left: 50%;
    bottom: 50%;
}

#a {
    background-color: blue;
    border: 2px solid red;
    position: absolute;
    right: -12px;
    top: -12px;
    left: -12px;
    bottom: -12px;
}